The present invention relates to a light quantity adjusting device for adjusting brightness of an image when a light source irradiates an image formed by image forming means such as a Braun tube or a liquid crystal panel so that the image is projected on a screen through a projecting lens. The present invention also relates to a projector apparatus using the light quantity adjusting device.
In a projector apparatus, an image such as a symbol and a picture is formed on an image forming unit such as a Braun tube (i.e., CRT) or a liquid crystal panel, and a light source such as a halogen lamp irradiates the image, so that a projecting lens projects the image on a screen. The projector apparatus projects a still image such as a symbol image on a screen for a presentation, or a motion picture on a screen of a home theater.
When the projector apparatus is used for a presentation or movie, an environment significantly affects a vision of a viewer depending on a bright room or a dark room. For example, when an image with low luminance is projected in a bright room, it is difficult to obtain a clear image. In contrast, when an image with high luminance is projected in a dark room, the image looks too bright. Further, when luminance of an image changes greatly and repeatedly for long time, i.e., from a dark screen to a bright screen, it is possible to pose a risk of fatigue of eyes or an optical stimulus. In particular, when the projector apparatus for a presentation requiring high luminance is used for a home theater, an image becomes too bright and a user may suffer eye fatigue.
Accordingly, it is necessary to properly adjust brightness of an image to be projected on a screen. When an image is projected in a dark room, it is necessary to reduce quantity of light. When an image becomes repeatedly bright and dark, for example, an image changes bright and dark for every one several tenth second, a viewer may suffer eye fatigue and receive an optical stimulus, thereby causing a physical problem. Accordingly, it is necessary to adjust the quantity of light for every frame of continuous images for reducing the stimuli on the eyes.
Japanese Patent Publication (Kokai) No. 2003-241311 has disclosed a device for adjusting light quantity. In the reference, light from a light source is divided into three primary colors R, G and B through a dichroic mirror. When light is irradiated on an image forming panel such as a liquid crystal panel, a light quantity reducing device is arranged between the light source and the dichroic mirror.
In the projector apparatus disclosed in the reference, light from the light source lamp is divided into the three primary colors R, G and B, and the primary colors are irradiated on the image forming panel formed of the liquid crystal panel. A projecting lens focuses light passing through the panel and projects an image on an outside screen. As a method of forming an image, other than the liquid crystal panel, there is known a method (a CRT projector) in which the Braun tube emits scanning lines or a digital imaging method (a digital light processing projector) in which fine mirror surfaces transform beams of the three primary colors R, G and B into scanning lines.
In the light quantity reducing device, a substrate having an optical path opening aligned with a center of an optical axis is arranged in an optical path from the light source to the mirror. A plurality of blades is sequentially overlapped at a circumferential edge of the optical path opening of the substrate, and is arranged to be rotatable. The blades are attached to the circumferential edge of the optical path opening with a predetermined spacing, and contour edge portions thereof are overlapped in a scale shape. Further, the blades are arranged such that leading end portions thereof face the optical path opening. When the blades rotate around end portions thereof, the leading end portions cover the optical path opening from a large aperture to a small aperture. Such a structure is widely known as a light quantity adjusting device for a camera.
However, the following problems may occur when such a structure widely known in a camera device, in which the plural blades arranged around the optical path opening and rotate to adjust an aperture of the optical path opening, is adopted in a projector apparatus such as a projector. In the camera device, when the blades for adjusting light quantity are opened and closed at a relatively low speed for preparing for shooting a picture, an image to be taken is hardly influenced. Also, similar to shutter blades, even if the blade members slide each other and generate an operation sound such as a clanking noise upon the opening/closing operation, there is no serious problem.
However, in the projector apparatus, when the light quantity adjusting blades are opened and closed (operated) and generate an operation sound, there may be a serious influence on an environment of a meeting or movie. In particular, when the blade members are made of thin metal sheets, it is possible to generate a large metallic noise. When the blades are operated for reducing luminance change of each image changing every 1/60 second, for example, it is necessary to move the blade members at a speed of several hundredth second. Accordingly, the operation sound of the blades is repeated all the time, thereby making a user uncomfortable. When the blades are operated at a lower speed to reduce the noise, it is difficult to adjust the light quantity to a change in an image, thereby causing image flickering.
In view of the problems described above, an object of the present invention to provide a light quantity adjusting device with a simple structure and a low price, in which it is possible to reduce an operation sound due to contact of a plurality of blades and adjust light quantity at a high speed when the blades adjust the light quantity in an optical path from a light source to a projecting lens through a large or small aperture.
Another object of the present invention is to provide a projector apparatus using the light quantity adjusting device.
Further objects and advantages of the invention will be apparent from the following description of the invention.